We used four herds at three Kansas ranches
to evaluate the potential of two new estrus
synchronization strategies to increase estrus
expression and fertility of 911 crossbred suckled
beef cows. The treatments included: 1) 100 μg
of GnRH and a 6-mg norgestomet ear implant
on day -7 and 25 mg of PG F2" and implant
removal on day 0 (GnRH+NORG+PG F2"); 2)
100 μg of GnRH on day - 7 and 25 mg of PGF 2"
on day 0 (GnRH+PG F2"); and 3 ) (control) 25-
mg injections of PG F2" on days -14 and 0;
(2×PGF2" control) . The GnRH+NORG+ PGF 2"
and GnRH+PGF treatments increased (P<.01) 2"
the overall percentages of cows detected in
estrus by 49% and 27% and pregnancy rates by
46% and 37%, respectively, over the control
group, without altering conception rate. Both
treatments increase d the estrus, conception, and
pregnancy rates of noncycling cows, compared
to controls.
